NOTE: This should also work with any other version of Photoshop, but some steps may be a slightly different.
Step 1: Find the images
The reason why it must be a PNG is because of the transparency and shadow. A JPEG or BMP image will not have the transparency you need.
Next, find an image that you will want to place onto the folder. In this case it is the Instructables Bot. This image doesn't really have to be a PNG, but it can make the job a lot easier if it is.